1. Field of the Invention
The present invention relates to a method for the production of olefin polymers having a high crystallinity.
2. Description of the Prior Art
It is well known that olefins can be polymerized by the so-called Ziegler-Natta catalyst comprising a compound of a transition metal in Groups IV to VI of the periodic table and a metal in Groups I to III in the periodic table or an organo-compound thereof. Most generally, the polymerization is carried out at less than about 100.degree. C., and the polymers are obtained in a slurry form.
In this polymerization process, amorphous polymers are produced as a by-product in addition to olefin polymers of high stereo-regularity which are very valuable industrially.
This amorphous polymer has a low industrial value and adversely effects the mechanical properties of products formed therefrom, for example, film, fiber and the like, of the olefin polymers.
Further, the formation of this amorphous polymer uselessly consumes the monomer raw material, and equipment for removal of the polymer become necessary. This is a very important disadvantage from an industrial point of view.
Consequently, it can easily be imagined that, if the formation of such polymer is substantially or completely inhibited, such would be very advantageous industrially.
In the polymerization process, on the other hand, the catalyst remains as a residue in the olefin polymers and adversely effects the stability and processability of the polymers. Accordingly, equipment for removal of the residual catalyst and stabilization of the polymers become necessary.
These disadvantages of the process can be improved by increasing the catalytic activity which is expressed by the yield of olefin polymer per unit weight of catalyst. Further, equipment for removal of the residual catalyst becomes unnecessary and thus a reduction in the manufacturing cost of the olefin polymer becomes also possible.
In the production of olefin polymers such as propylene polymers, butene-1 polymers and the like, titanium trichloride is most widely used as the transition metal compound which is a component of the solid catalyst.
Titanium trichloride used for such purpose is obtained by (1) reducing titanium tetrachloride with hydrogen, followed by activation by ball-mill powdering, (2) reducing titanium tetrachloride with metallic aluminum, followed by activation by ball-mill powdering (in this case, the resulting compound has the general formula TiCl.sub.3 (AlCl.sub.3).sub.1/3), or (3) reducing titanium tetrachloride with an organo-aluminum compound at -30.degree. to 30.degree. C. and heating the resulting solid reduction product at 100.degree. to 180.degree. C. to change the crystal form thereof.
Since, however, the titanium trichloride thus obtained is not sufficiently satisfactory in terms of catalytic activity and in terms of the stereo-regularity of the polymers produced, Japanese patent publication No. 92,298/1973 discloses an improvement in the titanium trichloride composition obtained by the reduction of titanium tetrachloride with an organo-aluminum compound, followed by heat treatment. That is, this improvement comprises powdering the above-described titanium trichloride composition and other compounds in a ball mill, followed by extraction-washing with a solvent. In this improved process, however, it is essential to pulverize the titanium trichloride composition in a ball mill. But the catalyst obtained by this process has insufficient catalytic activity.
An improvement in the catalytic activity of the titanium trichloride composition is also disclosed in Japanese patent publication No. 123,091/1975. This patent discloses an improvement in the solid complex catalyst disclosed in Japanese patent publication No. 34,478/1972. The former patent comprises treating the solid complex catalyst (titanium trichloride composition) with carbon tetrachloride.
In investigations leading to this invention, it was found, however, that the effect of the carbon tetrachloride treatment is not sufficient as will be shown later in the reference examples herein.
Further, Japanese patent publication No. 143,790/1975 discloses treatment of the solid resulting from the reduction of titanium tetrachloride with aluminum powder or an organo-aluminum compound with a mixture of a complexing agent and carbon tetrachloride. The disclosure is that after drop-wise adding an organo-aluminum compound to titanium tetrachloride at a temperature of -10.degree. to 10.degree. C., the reaction may be completed by increasing the temperature of the reaction mixture to 20.degree. to 100.degree. C., but preferably the reaction is completed by maintaining a low temperature without increasing the temperature. Since, however, the solid catalyst thus obtained is very unsatisfactory in terms of catalytic activity and with respect to the stereo-regularity of the polymers formed, it is desirable to repeat the carbon tetrachloride treatment once more.